ibook problem! Loud CPU fan, and no screen...

Today, my ibook randomly went to a black screen with lots of lines going down it, I tried to turn it off, but had to take the battery out. When I turned it on again, the screen wouldn't appear and I had a really loud sound from the CPU fan. Eventually it began to boot, but then went to black and shut off. Then it worked, right before i had an appointment with a genius, so I didn't go. Now it's doing the black screen and loud CPU fan again.

Any ideas about what the problem could be? I can't live without a laptop neye: